1. Field of the Invention
The invention relates to the field of forming contact openings in insulative layers, particularly plasma nitride layers used in the fabrication of semiconductor devices.
2. Prior Art
Plasma nitride (Si.sub.x /N.sub.y) is most often used as a passivation layer formed over a final metal layer in semiconductor devices. It is typically used for low temperature "rear-end" processing. Thus, for the most part openings such as those needed for contacts are not formed through this layer.
It is often necessary in the fabrication of semiconductor devices to form contacts through insulative layers. For example, openings are etched through a glass layer (doped SiO.sub.2) and then metal contacts are formed through the openings. These contacts can interconnect metal lines with substrate regions, interconnect metal or polysilicon members on one level with metal or polysilicon members on another level, and so on. It is well recognized that sharp corners in these openings can cause problems within the metalization. Typically, these corners result in high stress or thin regions in the metal which regions more readily crack. For a discussion of this problem and prior art solutions see "Investigation of Microcircuit Surface Metallurgy", 1969 Electronic Components Conference, Apr. 30-May 2, 1969, beginning at page 304; IBM Technical Disclosure Bulletin, Vol. 9, No. 4, September, 1966, entitled "Glassed Diode Aluminum Ohmic Contact"; and U.S. Pat. No. 3,825,442.
The present invention describes a process for forming a plasma nitride layer and opening therethrough which opening has tapered sides. This more readily permits the forming of contacts in the opening since better metal flow is obtained and high stress regions are minimized.